Generally, a barrier rib for a PDP is a structure formed in a dielectric layer, which is commonly provided on an electrode layer, formed on a rear glass substrate having address electrodes patterned to be parallel to each other. The barrier rib functions to maintain a discharge distance in the panel and to prevent electrical and optical interference between adjacent cells, and has a width of 40˜100 □ and a height of 50˜200 □.
In order to manufacture the barrier rib of a PDP, a frit material composed mainly of low melting point glass is used in a slurry or paste phase. Techniques for the formation of a barrier rib using such a material include, for example, a screen-printing process, a sandblasting process, a photolithographic process, and a molding process.
The paste or slurry of the frit material is prepared in the shape of a barrier rib and is then sintered at a high temperature of 500˜600° C. to cure the glass frit. When Pb, serving as a representative softening material, is not added, a sintering process should be conducted at a higher temperature. However, among barrier rib materials, Pb at 500° C. or higher acts as an environmental pollutant. In the case where large amounts of waste are generated, as when manufacturing the barrier rib of a rear substrate, costs of treatment of environmental pollutants and waste are increased. Further, repeated high-temperature process for use in manufacturing a barrier rib suffers because the dimensions of the glass substrate vary, a non-uniform pattern is formed, the defect rate of a PDP is increased, and the screen size of the panel is difficult to enlarge. Thus, the PDP substrate supporting the barrier rib should also be formed of specific glass which does not soften at high temperatures.
A conventional 42-inch panel has been manufactured by preparing a dielectric layer as high as the barrier rib using a screen-printing process and then forming a barrier rib structure using a sandblasting process. However, when manufacturing PDPs, such as HDTVs, having 60-inch panels or larger, not only smaller pitches between the structures but also flatness are required. Hence, a screen-printing process through multi-layer printing and a sandblasting process are unsuitable for the fabrication of complicated structures having accurate dimensions. With the aim of overcoming the complication of the process due to multi-layer screen printing and realizing the formation of uniform barrier ribs over the entire panel, Japanese Patent Laid-open Publication Nos. 9-102273 and 10-291834 disclose a method of manufacturing a barrier rib layer through a single process using a transfer film (a composite film comprising a film forming material layer formed using a glass paste composition and a support film, and a cover film laminated on the film forming material layer to be easily removed). Although this method is advantageous because the process is simple, it has the drawbacks, such as limited use of the sintered low melting point glass as a substrate, difficulty in the formation of a fine pattern structure, poor surface flatness, generation of large amounts of environmental waste, etc. Therefore, there is a need for the development of a material that may be formed into a thick film through a single process and may easily form fine patterns, in order to manufacture a PDP having a large area and high image quality.
In manufacturing a PDP barrier rib, in addition to a conventionally used sandblasting process, a mold- or roll-pressing process may be used, which is advantageous in terms of realizing excellent quality of the resultant barrier rib, simplified manufacturing processes, and decreased manufacturing costs. This process is conducted by applying a paste containing a barrier rib material on a glass substrate or a metal substrate such as titanium and then drying it, or by laminating a dry film, followed by pressing the dried paste or the dry film using a flat type mold or a cylindrical roll type mold having a pattern shape, which is opposite to that of a barrier rib, thereby forming a desired barrier rib. Technical contents regarding the above process are disclosed in Japanese Patent Laid-open Publication Nos. 11-185605 and 10-3265712, Japanese Patent Application No. 9-170148, and Korean Patent Application Nos. 1998-54538, 1998-21101, 1998-22675, and 1998-18584. Typically, the paste contains inorganic material (glass frit, loading ceramics (Al2O3, TiO2, ZrO2, etc.)) as the barrier rib material, and further includes organic material (solvent, binder, thixotropic agent, plasticizer, diluent, other additives) to obtain fluidity required for printing and pressing. The paste thus obtained is dried and then pressed using a flat type mold having a pattern shape, which is opposite to that of the barrier rib to be manufactured, to form a barrier rib, which is then removed from the mold and sintered. Subsequently, a phosphor is printed on side surfaces and a lower surface of the barrier rib, thus completing a rear substrate of a PDP. In these methods, however, the release of the mold from the formed barrier rib is difficult to assure.
Likewise, methods of manufacturing a barrier rib are proposed using a roll having grooves as a pattern having a shape opposite to that of a barrier rib, instead of the flat type mold. This method is conducted in a manner such that the dried paste or dry film is pressed in the shape of a barrier rib using the roll, and then sintered, thereby manufacturing a desired barrier rib.
Other than such mechanical pressing processes, Japanese Patent Application Nos. 9-165907 and 9-243523 and Korean Patent Application No. 1998-34029 disclose methods of manufacturing a barrier rib, comprising processing a metal or polymer material using a flat mold or roll or molding it using a photo etching process to have a pattern having a shape opposite to that of a barrier rib, loading a paste or slurry containing a barrier rib material into the pattern, drying the loaded paste or slurry and then removing the mold, which was proposed as a technique for forming a fine barrier rib. Further, grooves as a pattern corresponding to the shape of a barrier rib are formed through a photolithographic process or a mold pressing process, and are then filled with a barrier rib material. In this case, the filling procedure is carried out using a printing process using a squeezer or a tape casting process. After the barrier rib material is loaded, it is dried and laminated on a substrate having address electrodes printed thereon. The mold is released, and the barrier rib is sintered and is then printed on side surfaces and a lower surface thereof with the use of a phosphor, to manufacture a desired rear substrate of a PDP.
In the molding process, the problems regarding fluidity of the barrier material applied on the mold and, as well, reactivity between the barrier rib material and the mold, or release there between upon removing the mold from the formed barrier rib negatively affect the manufacture of the barrier rib. Further, when the mold is filled with the barrier rib material, all pattern grooves of the mold should be uniformly filled with the material in order to form a uniform barrier rib. When the mold is removed, the sintered barrier rib material in the patterns of the mold should have no reactivity with the mold in order to be easily released from the mold, to obtain non-degraded uniform barrier ribs. However, it is difficult to achieve such objects using the conventional methods.